70 



VOLCANOES. 



that surround the summit and the crater's 

 mouth, the walls of the ashy cone are some- 

 times heated through, when the entire mount- 

 ain presents the most threatening and ill-omen- 

 ed aspect of inky black. 



The crater which, except in very rare cases, 

 occupies the summit of the volcano, forms a 

 cauldron-like, and often accessible valley, whose 

 bottom is subject to incessant changes. The 

 greater or less depth of the crater is, in many 

 volcanoes, an indication of the proximity or re- 

 moteness of an eruption. In the cauldron-like 

 crater extensive fissures open and close again 

 alternately ; through these vapours of various 

 kinds find vent, or small rounded fiery throats, 

 filled with molten matters, are formed upon 

 them. The ground rises and falls, and on it 

 are piled hillocks of ashes and cones of erup- 

 tion, which occasionally rise high above the 

 edges of the crater, and give the volcano its 

 characteristic physiognomy for years ; but on 

 the occurrence of fresh eruptions, they sink 

 suddenly down, and disappear. The openings 

 of these cones of eruption, which rise from the 

 floor of the crater, must not, as is too frequent- 

 ly done, be confounded with the crater itself, 

 which encircles them. When the crater is in- 

 accessible, from its vast depth, and the perpen- 

 dicular inward slope of its sides, as in the case 

 of Rucu-Pichincha (14,946 feet high), one can 

 still look down from the edges, upon the sum- 

 mits of the monticules which rise within the 

 cauldron-like crater, partially filled with sul- 

 phureous vapours. A more wonderful or grand- 

 er natural prospect I have never enjoyed. In 

 the interval between two eruptions, the crater 

 of a volcano may exhibit no luminous phe- 

 nomenon, but merely open fissures and jets of 

 watery vapour ; or hillocks of ashes that can 

 be approached without danger, are found upon 

 its scarcely heated bottom. These often grati- 

 fy the wandering geologist, without making 

 him run any risk, by casting out glowing mass- 

 es, which fall on the edges of the cone of sco- 

 riae, their appearance being regularly announ- 

 ced by slight, and entirely local shocks — earth- 

 quakes on a small scale. Lava occasionally 

 flows from open fissures, or small fiery gorges, 

 into the crater itself, without bursting through 

 its walls, or overflowing its edges. But if it 

 does break through, the molten spring general- 

 ly flows smoothly, and in such a determinate 

 direction, that the great cauldron-like valley, 

 called the crater, can still be visited during the 

 period of the eruption. Without a particular 

 description of the conformation, and also of 

 the normal structure of burning mountains, 

 phenomena cannot be rightly comprehended 

 which have been distorted by fantastical de- 

 scriptions, and the various significations at- 

 tached to the words crater, volcano, and cone ; 

 or, rather, to the indefinite and indeterminate 

 use of these words. The edges of the crater 

 sometimes show themselves much less liable 

 to change than might be expected. A compari- 

 son of De Saussure's measurements with my 

 own, yields the remarkable result, in connection 

 with Vesuvius at least, that the north-west 

 edge of the volcano, the Rocca del Palo, may 

 be regarded as having remained for forty-nine 

 years (1773-1822) almost without change in its 

 elevation above the level of the sea. Any dif- 



ference that appears may be looked on as with 

 in the possible errors of measurement("'). 



Volcanoes which lift their summits far above 

 the limits of eternal snow, like those of the 

 Andes, present a variety of peculiar features. 

 The sudden melting of the snow in the course 

 of an eruption, not only occasions destructive 

 floods, torrents in which heaps of smoking ash- 

 es are floated away on blocks of ice ; but the 

 accumulation of ice and snow goes on produ- 

 cing its influence uninterruptedly, and by fil- 

 tration into the trachytic rocks, even whilst 

 the volcano is perfectly quiescent. Caverns 

 are thus gradually produced on the declivities 

 or at the foot of the burning mountain, and 

 these become subterraneous reservoirs of wa- 

 ter, which communicate in various ways, and 

 by narrow mouths, with the Alpine rivulets of 

 Quito. The fishes of these Alpine streams 

 multiply greatly, particularly in the gloom of 

 the caverns ; and then, when the earthquakes 

 come, which precede all eruptions of volcanoes 

 in the Andes, and the whole mass of the mount- 

 ain is shaken, the subterraneous caverns at 

 once give way, and pour out a deluge of water, 

 fishes, and tufaceous mud. This is the singu- 

 lar phenomenon which the presence of the 

 Pimelodes Cyclopum(^'''), the Prenadilla of the 

 inhabitants of the lofty plains of Quito, attests. 

 When, in the night between the 19th and 20th 

 of June, 1698, the summit of Carguairazo, a 

 burning mountain 18,000 feet high, crumbled 

 together, so that no more than two enormous 

 rocky horns of the crater's edge remained, the 

 country for nearly two square miles was deso- 

 lated with liquid tuff and argillaceous mud 

 (lodazales) inclosing dead fishes. So also was 

 the putrid fever of the mountain town, Ibarra, 

 to the north of Quito, which occurred seven 

 years before, ascribed to an eruption of fish 

 from the volcano Imbaburu. 



Water and mud which, in the volcanoes of 

 the Andes, do not pour down from the crater 

 itself, but from cavities in the trachytic mass 

 of the mountain, ought not, consequently, in 

 the strict sense of the phrase, to be reckoned 

 among the number of proper volcanic phenom- 

 ena. They are only mediately connected with 

 the activity of volcanoes, nearly in the same 

 measure as the irregular meteorological pro- 

 cess, which, in my earlier writings, I have spo- 

 ken of under the title of the Volcanic storm. 

 The hot, watery vapour which rises from the 

 crater, and mingles with the atmosphere during 

 the eruption, forms a cloud as it cools, with 

 which the column of ashes and fire, many thou- 

 sand feet in height, is surrounded. So sudden 

 a condensation of vapour, and the production 

 of a cloud of enormous superficial dimensions, 

 increase the electrical tension, as Gay Lussac 

 has shown. Forked lightnings dart from the 

 column of ashes, and the rolling thunder of the 

 volcanic storm is then plainly distinguishable 

 from the rumbling in the interior of the mount- 

 ain. This was well observed towards the end 

 of the eruption of Vesuvius in the month of 

 October, 1822. The lightning, which proceed- 

 ed from the volcanic steam-cloud of the Katla- 

 gia burningrmountain in the Island of Iceland, 

 according to Olaffen's account, upon one occa- 

 sion (17th October, 1755), killed eleven horses 

 1 and two men. 



